There are various types of communication apparatuses having functions of performing communication through a telephone network (a switch board and so on) such as a telephone function and a facsimile function (hereinafter referred to as “telephone-network communication function”). For example, there are single-use machines having the telephone-network communication function, as well as so-called multifunction peripherals having a print function and a copy function in addition to the telephone-network communication function.
These communication apparatuses generally have a main power-supply circuit for supplying various units in the apparatus with electric power. For example, in a multifunction peripheral, when a power switch is turned on, the main power-supply circuit supplies electric power to various units in the apparatus, such as a print mechanism, a copy mechanism, various communication circuits such as a DAA (Data Access Arrangement) and a modem, and a control circuit that controls operations of these mechanisms, thereby making the various units in the apparatus in operable states.
Recently, for reducing power consumption, various electrical equipment including communication apparatuses is provided with, as operational modes, a normal mode in which the main power-supply circuit supplies various units with electric power (or a state in which electric power can be supplied) and a sleep mode in which power supply from the main power-supply circuit is stopped except that micro power is supplied to a requisite minimum circuit such as a control circuit.